<template>
  <ul class="list" :style="{height: h + 'px'}">
    <li class="item"
      v-for="item of letters"
      :key="item"
      :ref="item"
      @click="handleLetterClick"
      @touchstart.prevent="handleTouchStart"
      @touchmove="handleTouchMove"
      @touchend="handleTouchEnd"
    >
      {{item}}
    </li>
  </ul>
</template>

<script>

export default {
  name: 'CityAlphabet',
  props: {
    cities: Object
  },
  data () {
    return {
      touchStatus: false,
      startY: 0,
      timer: null,
    }
  },
  updated () {
    this.startY = this.$refs['A'][0].offsetTop
  },
  computed: {
    letters () {
      const letters = []
      for (let i in this.cities) {
        letters.push(i)
      }
      return letters
    },
    /*键盘弹出时字母表会被挤压，因此给字母表的包裹元素list高度设置为clientHeight的高度*/
    h () {
    this.bodyHeight = document.documentElement.clientHeight
    return this.bodyHeight
    }
  },
  methods: {
    handleLetterClick (e) {
      this.$emit('change',e.target.innerText)
    },
    handleTouchStart () {
      this.touchStatus = true
    },
    handleTouchMove (e) {
      if (this.touchStatus) {
        if (this.timer) {
          clearTimeout(this.timer)
        }
        this.timer = setTimeout(()=>{
          const touchY = e.touches[0].clientY
          const index = Math.floor((touchY - this.startY) / 24)
          if (index >= 0 && index < this.letters.length) {
            this.$emit('change',this.letters[index])
          }
        },16)
      }
    },
    handleTouchEnd () {
      this.touchStatus = false
    }
  }
}

</script>

<style lang="stylus" scoped>
  .list
    display: flex
    flex-direction: column
    justify-content: center
    position: absolute
    top: 0
    right: 0
    bottom: 0
    .item
      list-style-type:none
      font-size: 1rem
      width: 2rem
      text-align: center
      color: #007bff
</style>




